Automatic antenna switching diversity system



y 1941' I H. o. PETERSON 2,243,118

AUTOMATIC ANTENNA SWITCHING DIVERSITY SYSTEM Filed March 15, 1939 2 Sheets-Sheet 1 1 .1

RECEIVER I 2 3 4 23 5 r--A|/c VOLTAGE I) 'L l l l- 27 INVENTOR.

0. PETERSON ATTORNEY.

y 1941- H. o. PETERSON 2,243,118

AUTOMATIC ANTENNA SWITCHING DIVERSITY SYSTEM Filed March 15, 1939 2 Sheets-Sheet 2 INVENTOR.

HA 0? 0. PETERSON BY ATTORNEY.

Patented May 27, 1941 AUTOMATIC ANTENNA SWITCHING DIVERSITY SYSTEM Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 15, 1939, Serial No. 261,948

Claims.

To date, the use of diversity reception in amateur and home receivers has been very much limited by the added expense of providing two or more receivers for reception of a given signal. The invention relates to a diversity system in which only one receiver is required, A switching arrangement is provided whereby the input of the receiver can be connected to either one of two receivers.

Generally speaking, the quality of a fading signal is satisfactory when the signal strength is either normal or above normal, and the quality becomes bad whenthe signal fades into a deep depression below normal. For that condition, it very often happens that the carrier itself fades much deeper than the side bands and the signal at the detector is deficient in carrier voltage, resulting in the same effect as over-modulation. However, it has been found that while a signal may be fading strongly in one location, at another location only a short distance away the signal may be of normal amplitude or even increasing in strength. The same efiect may also be observed between two antennas of different characteristics at a single location. 7

An object, therefore, of the present invention is to provide means for automatically switching a receiver from an antenna in which the signal strength has fallen to a predetermined minimum to a second antenna receiving the same signal but in which the signal may be of greater amplitude.

Another object of my invention is to provide switching means, as aforesaid, in which the changeover takes place when side band voltages exceed carrier voltage. The receiver remains switched over to the other antenna until the undesired conditions again occur whereupon the receiver input is switched back to the first antenna.

An embodiment of my invention includes structure responsive to the developed automatic volume control voltage in a receiver for actuating either a mechanical relay or a pair of thermionic relay for switching the receiver from one antenna to another either at the same location but of different characteristics, or at a difierent geographical location. In a modified form of the invention the switching of-antennas is responsive to a comparison between rectified carrier voltage and the rectified signal in said carrier.

Reference will now be had, for a more complete understanding of my invention, to the following detailed description, which is 'accompanied by drawings in which Figure 1 shows diagrammatically an embodiment of the invention, Figure 2 shows a modification thereof and Figure 3 shows another embodiment of the inventlon.

Referring to Figure 1, I have shown a receiver I which is provided with a conventional loud speaker (not shown) and some form of automatic volume control in which a control voltage becomes less negative when the carrier voltage decreases. The control voltage is available at terminals 2 and 3. The input 4 to the receiver may be switched to one of two antennas 5, 6 provided, by means of the mechanical relay I represented by coils 9 and I0, movable blades H and I2 and stationary contacts l3, l4, l5 and 16. The movable blades ll, [2 are connected to the input 4 of the receiver. One set of stationary contacts l3, I4 are connected to antenna 5 by means of transmission line I! and the other set of contacts l5, l6 are connected to antenna 6 by means of transmission line IS. The current for operating the relay is controlled by grid controlled tubes 20 and 2| which may preferably be gas triodes and are so shown. Each of these gas triodes has the property of remaining at cut-01f as long as the grid is held at a voltage of more than a certain negative value.

When the grid voltage is made less than this amount negative the tube starts drawing current and continues to draw current until the plate voltage is made less than some small positive voltage, irrespective of the condition of grid voltage. a

In the circuit shown the two gas triodes are connected with their plates in a push-pull circuit and their grids in parallel. Assuming that at the moment one of these tubes is drawing current and the other tube is not drawing current from plate battery22 and both grids are biased negative to a point beyond cut-ofi. Assume, for example, that tube 20 is drawing current and tube 24 is not drawing current, There will be, for this condition, a voltage drop through resistor 23. Now if the two grids are made less negative a point will be reached where tube 2| will commence to draw plate current quite suddenly. This sudden flow of plate current in tube 2| will result in a sudden dip in the voltage at the plate of tube 2| due to the voltage drop in resistor 24 when current flows through it. This voltage dip is coupled over to the plate of tube 20 through the coupling condenser 25, which will momentarily cause the plate voltage of tube 20 to reach a value near zero or perhaps slightly negative, causing plate current to cease flowing in tube 29. Thus plate current has stopped in tube 20 and commenced in tube 2|, which will result in switching the receiver over to the other antenna. It is assumed that due to diversity action of fading, the signal in antenna 6 will not fade at the same time as in antenna 5 so when the receiver is switched over to antenna 6 the grids of tubes and 2| will again go negative beyond cut-off because of the greater signal strength in that antenna. Thus the condition of current flow in tubes 20 and 2| will remain constant until the signal again fades to a point where the automatic volume control potential falls below a predetermined negative value. This value may be adjusted by means of a bias potentiometer 26 operating in conjunction with a voltage supply 21. It will be necessary to make condenser and resistors 22 and 24 large enough so that the relay and automatic gain control voltage'can operate before a condition of oscillation takes place in the circuit of the gas triodes. This oscillating tendency can be further reduced by the provision of a time constant circuit in the grid circuit as shown in Figure3 and which will be described in more detail in connection therewith.

Figure 2 shows a modification of the circuit of Figure 1 in which the flow of signal energy to receiver is controlled through vacuum tubes 42 and 43 having their plate circuits connected together and coupled to the input of receiver l by coupling condenser 40. Plate voltage is supplied to tubes 42, 43 through choke 4!. The grid circuits of tubes 42, 43 are coupled by tuned antenna transformers 46, 41 and transmission lines l1, l9 to antennas 5 and 5. Since transformers 46, 41 are always to be tuned to the same frequency their tuning condensers may be ganged as shown. The gas triodes 20 and 2| serve to bias one or the other of tubes 42 and 43 to cut-off.

For instance, at a given moment current will be flowing in the plate circuit of tube 20, through resistance 29, which will make the plate voltage of tube 20 more negative than the plate voltage of tube 2|. This negative voltage is transmitted through resistance 3| to condenser 33 and resistance 35, resulting in a large negative bias at the grid of tube 43, so it will not at the moment pass signal from antenna 6 to the receiver input circuit 40. At this moment tube 2| is not drawin current so the voltage at the plate of tube 2| is substantially the same as the voltage across the power supply 21. This more positive voltage is transmitted through resistance: 32 in conjunction with time constant circuit 34, and the negative bias provided by 31, 38 and 39, to result in a grid voltage on tube 42 of such value that this tube will at the moment pass signal from antenna 5 into the receiver. 'The switching action in tubes 20 and 2| is controlled by the carrier voltage in a manner similar to that shown in Figure 1 and completelydescribed heretofore with reference to that figure.

In Figure 3 I have shown substantially the same type of antenna switching apparatus, as in Figure 2, but the control is suchthat the switchover takes place whenever the side band voltages exceed the carrier voltage, that is, whenever modulation exceeds 100%.

In the radio receiver I which we may assume is a superheterodyne, intermediate frequency voltage IF appearing in transformer is rectified by rectifier 5| to produce a voltage drop in resistor 53. Across resistor 53 also appears the audio frequency voltages caused by modulation of the transmitter. This audio frequency voltage is coupled to amplifier tube 56 which feeds audio frequency through transformer 59 into rectifier 6Q producing a unidirectional voltage in resistor 62. The rectifier circuits 58, 62 are connected so that the voltage feeding into resistor 63 is positive with respect to ground. The voltage fed into resistor 52 is negative with respect to ground.

Thus if the rectified audio voltages exceed the rectified carrier, 'the grids of gas triodes 20 and 2| will become positive and a switch-over will take place according to the manner previously outlined in the description of Figure 1. When the switch-over takes place the negative impulse in the plate circuit of each gas triode is coupled to its grid circuit by means of condensers 65, 61 sending it negative and placing a negative charge on condenser so that there will be no tendency for another switch-over in tubes 25 and 2| until after an interval of time has elapsed, long enough for the receiver to become established in operation on the other antenna. Unilateral conductance devices such as diodes 68 and 69 may be placed across condensers 66 and 61, as shown in Figure 3, in order to place a more definite charge on the grids when changeover occurs. While I have shown diode rectifier tubes across condensers 56 and 51, it should be understood that any other suitable unilaterally conducting device may be used. However, these rectifiers may not under all circumstances be necessary particularly when a more simple and inexpensive device is required. Condenser 25 may also be made large enough so that the tendency of tubes 20 and 2| to oscillate during switch-over conditions is substantially eliminated.

While I have shown and particularly described several modifications of my invention, it is to be clearly understood that the scope of my invention is not to be limited thereto but that modifications and alterations within the scopeof my invention may be made.

What I claim and desire to secure by Letters Patent is:

1. In a diversity system a pair of antennae, a receiver having means therein for developing a potential proportional to the amplitude of signals applied to an input circuit of said receiver, means including a pair of gas discharge tubes so connected in an opposing relationship that only one of said tubes is conductive at any instant, means for applying said potential to said tubes in such manner that a drop in said potential causes the non-conductive tube to become conducting and the other to cease conducting and means coupled to each of said tubes for connecting one of said antennae to the input of said receiver.

2. In a diversity system a pair of antennae, a lecelvel having means therein for developing a negative potential proportional to the amplitude ofsignals applied to an input circuit of said receiver, means including a, pair of grid Controlled as discharge tubes so connected in an opposing relationship that only one of said tubes is conductive at any instant, means for applying said e a ve potential to the grids of said tubes in such manner that a drop in said potential causes the non-conductive tube to become conducting and the other to cease conducting, and me coupled to each of said tubes for connecting one of said antennae to the input circuit of said receiver.

3. In a diversity system a pair of antennae, a

receiver having means therein for developing a negative potential proportional to the amplitude of signals applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and a plate, means for connecting said plates to an output circuit in an opposing relationship, means for so connecting said grids in parallel and means for energizing said tube electrodes that at any time one of said tubes is conducting and the other is non-conducting,

means for so applying said negative potential to receiver having means therein for developing a negative potential proportional to the amplitude of signals applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and a plate, means for connecting said plates to a pair of windings of a relay in an opposing relationship, means for so connecting said grids in parallel and means for energizing said tube electrodes that at any time one of said tubes is conducting and the other is non-conducting, means for so applying said negative potential to said grids that a drop in said potential causes said tubes to interchange their conducting conditions, contact means carried by an armature of said relay and connected to said input circuit and stationary cont-acts associated with said armature and connected to each of said antennae whereby said antennae are selectively connected to said output circuit.

5. In a diversity system a pair of antennae, a receiver having means therein for developing a negative potential proportional to the amplitude of signals applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and a plate, means for connecting said plates to an output circuit in an opposing relationship, means for connecting said grids in parallel and means for energizing said tube electrodes, means in said output circuit so arranged that at any time one of said tubes is conducting and the other is non-conducting,

means for so applying said negative potential to said grids that a drop in said potential causes said tubes to interchange their conducting conditions, a pair of thermionic discharge tube amplifier circuits each having an input and an output, their inputs being connected to said antennae and their outputs being connected to said receiver input, means for coupling each of said amplifier circuits to one of said gas discharge tubes said last mentioned means being so arranged that only the amplifier circuit associated with the conducting one of said gas discharge tubes is biased to cut-ofi.

6. In a diversity system a pair of antennae, a receiver having means therein for developing a negative potential proportional to the amplitude of signals applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and 'a plate, means for connecting said plates to an output circuit in an opposing relationship, means for connecting said grids in parallel, means for energizing said tube electrodes and means connected to said plates for preventing more than one of said tubes from conducting at any time, means for so applying said negative potential to said grids that a drop in said potential causes said tubes to interchange their conducting conditions, a pair of thermionic discharge tube amplifier circuits each having an input and an output, said inputs being connected to said antennae and said outputs being connected to said receiver input, each of said amplifier circuits being so associated with one of said gas discharge tubes that only the amplifier circuit coupled to the conductive one of said gas discharge tubes is biased to cut-ofi.

'7. In a diversity system a pair of antennae, a receiver having means therein for developing a negative potential proportion-a1 to the amplitude of signals applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and a plate, an output circuit for each of said plates, means for connecting said output circuits in an opposing relationship, means for connecting said grids in parallel, means for energizing said tube electrodes and means connected to said plates whereby only one of said tubes is conductive at any time, means for so applying said negative potential to said grids that a drop in said potential causes said tubes to interchange their conducting conditions, an antenna coupling circuit connected to each of said antennae, a pair of grid controlled thermionic discharge tubes each having an anode and a control grid, each of said control grids being coupled to one of said pair of coupling circuits connected to said antennae, said anodes being connected in parallel and coupled to said receiver input, a connection from each of said coupling circuits to an output circuit of said gas discharge tubes whereby current flow through said output circuit places a cut-off bias on the thermionic discharge tube associated therewith.

8. In a diversity system a pair of antennae, a receiver having means therein for developing a negative potential proportional to the amplitude of a carrier applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and a plate, means for connecting said plates to an output circuit in an opposing relationship, means for connecting said grids in parallel and means for energizing said tube electrodes said last mentioned means and said output circuit being so arranged that at any time only one of said tubes is conducting and the other is non-conducting, means for applying said negative potential to said grids, means for developing from modulation on said carrier a second potential proportional to amplitude of said modulation, means for applying said second potential to said grids in an opposing relationship 7 to said first potential whereby an increase in said second potential with respect to said first potential over a predetermined amount causes said non-conducting tube to conduct and said conducting tube to cease conducting, a pair of thermionic discharge tube amplifier circuits having their inputs connected to said antennae and their output connected to said receiver input, each of said amplifier circuits being so coupled to one of said gas discharge tubes that'only the amplifier circuit coupled to the conducting one of said gas discharge tubes is biased to cut-off.

9. In a diversity system a pair of antennae, a receive having means therein for developing a negative potential proportional to the amplitude of a carrier applied to an input circuit of said receive, a pair of gas discharge tubes each having at least a grid and a plate, means for connecting said plates to an output circuit in an opposing relationship, means for connecting said grids in parallel, means for energizing said tube electrodes and means in said output circuit so arranged that only one of said tubes is conductive at any time, means for applying said negative potential to said grids, means for developing from modulation on said carrier a second potential proportional to amplitude of said modulation, means for applying said second potential to said grids in an opposing relationship to said first potential whereby an increase in said second po-' tential with respect to said first potential causes the non-conductive tube to become conductive, a pair of thermionic discharge tube amplifier circuits having their inputs connected to said antennae and their output connected to said receiver input, each of said amplifier circuits being so coupled to one of said gas discharge tubes that only the amplifier circuit coupled to the conductive one of said gas discharge tubes is biased to cut-off.

10. In a diversity system a pair of antennae, a receiver having means therein for developing a negative potential proportional to the amplitude of a carrier applied to an input circuit of said receiver, a pair of gas discharge tubes each having at least a grid and a plate, an output circuit for each of said plates, means for connecting said output circuits in an opposing relationship, means for connecting said grids in parallel, means for energizing said tube electrodes, said output circuits being so connected that only one of said tubes is conductive at any time, means for applying said negative potential to said grids, means for developing from modulation on said carrier a second potential proportional to amplitude of said modulation, means for applying said second potential to said grids in an opposing relationship to said first potential whereby an increase in said second potential with respect to said first potential causes the non-conductive tube to become conductive, an antenna coupling circuit connected to each of said antennae, a pair of grid controlled thermionic discharge tubes each having at least an anode and a control grid, each of said control grids being connected to one of said pair of coupling circuits connected to said antennae, said anodes being connected in parallel and coupled to said receiver input circuit, a connection from each of said coupling circuits to an output circuit of said gas discharge tubes, said connections being so arranged that current flow through either of said output circuits places a cut-off bias on the control grid of one of said thermionic discharge tubes.

HAROLD O. PETERSON. 

